Pressure gain valveless combustior



Sept. 5, 1961 C. D. PORTER ETAL PRESSURE GAIN VALVELESS COMBUSTOR Filed July 29, 1958 2 Sheets-Sheet 1 INVENTORS CAR ROLL D. PORTER MAR 10 A. PERS ECH INO m ATTORNEYj Sept. 5, 1961 c. D. PORTER ET AL 2,998,705

PRESSURE GAIN VALVELESS COMBUSTOR Filed July 29, 1958 2 Sheets-Sheet 2 INVENTOR) CARROLL D. PORTER MARIO A. PERSECHINO MMATTORNEYJ United States Patent ce 2,998,705 PRESSURE GAIN VALVELESS COMBUSTOR Carroll D. Porter and Mario A. Persechino, Chesapeake,

Md., assignors to the United States of America as represented by the Secretary of the Navy Filed July 29, 1958, Ser. No. 751,808 6 Claims. (Cl. 6035.6) (Granted under Title 35, US. Code (1952), see. 266) Heretofore, pulse jet engines of the valveless type have been constructed and operated satisfactorily; however, many problems exist in adapting a valvele'ss pulse combustor for use with a gas turbine combustor system without great losses in the volumetric efliciency.

gether. with the hotter main flow into the tail-ejector section which is expanded'into a pressurized flow reservoir which has a discharge opening into the working zone (turbine for power, ice to be melted etc.).

Referring nowfto the drawings wherein like reference.

. characters represent like parts throughout, there is shown by illustration in FIG. 1 a pulse jet combustor inlet system 10 which comprises a housing 11 defining a plenum chamber having an air inlet 12. A pulse combustor inlet tube 13 is positioned in coaxial alignment with aninlet exhaust tube 14 and positioned within the plenum chamher 11 and supported by struts-15 secured to the housing 11. The adjacent ends of the tubes are rigidly supported in the struts and the outer end of the inlet exhaust tube is mounted for a sliding fit within a ring 16 connected to the struts. The combustor inlet tube and inlet exhaust tube are spaced from each other at 17 to permit flow of air into each of the tubes. The forward end of the pulse combustor inlet tube that permits fuel-air mixture to enter the combustion zone 18 of a valveless pulse jet 19 enters the combustion chamber at an angle such that minimum'blow-back through the air inlet tube occurs It is therefore an object of the present invention to increase the efiiciency of a valveless pulse jet combustor.

Another object of the invention is to improve the air inlet system of a pulse jet engine.

Still another object is to provide a valveless pulse jet engine capable of use as a combustor element for gas tur-.

bine engines.

Yet another object of the present invention is to increase the pressure at the outlet of the pulse combustor above that at the inlet.

Other and more specific objects of the invention will become apparent upon a careful consideration of the following detailed description when taken together with the accompanying drawings in which:

FIG. 1 illustrates the air inlet system in accordance to the present invention;

FIG. 2 illustrates an example of a pulse jet combustor in combination with the air inlet system illustrated by FIG. 1;

FIG. 3 is a modification of the device shown by illustration in FIG. 2; and

FIG. 4 is still another modification of the device shown by illustration in FIG. 2.

This invention is a combustor system which admits air through an inlet, combustor part of the air in a valveless pulse combustor, and discharges a mixture of air and combustion products through an outlet at a higher total pressure than exists at the inlet. The inlet system has a main air inlet, a valveless pulse combustor inlet tube, means defining a plenum chamber, an inlet exhaust tube, and an inlet ejector section. The backflow pulses from the combustor shoots through the pulse combustor inlet tube into the inlet exhaust tube, emerges and drives air entrained in the ejector section down into the expanding section of the ejector thus inducing a continued fresh air flow into the plenum chamber from the inlet which carries the products escaping the inlet tube along in a scavenging action. When the pulse tube reaches the negative part of the cycle the fresh air surrounding the pulse tube inlet rushes into the combustor inlet undiluted by blown back products. The inlet ejector may be connected to a duct surrounding the main pulse burner tube, furnishing a cooling gas which surrounds the hot burner. This gas flows along the tube length to the tail section of the combustor. Here it may enter a storage plenum where it is used periodically to furnish tail backfiow gas tolthe pulse burner tailpipe 'F-rom here it is shot toduring operation. A satisfactory tube end is described and shown in Patent No. 2,795,105; however, and satisfactory. tube ending can be used to carry out the teaching of the present invention. The rearward end of the inlet exhaust tube is spaced from the plenum chamber housing by the struts 15 and ends at an inlet exhaust ejector section 21 which increases in inside diameter away from the rearward end of the exhaust tube to permit expansion of the gas and air mixture in the ejector expanding section.

It is very important for efiicient operation that the distance between the adjacent ends of the pulse combustor inlet tube and the inlet exhaust tube remain constant so that the same amount of air can pass therethrough at all times. Thus the tall end of the inlet exhaust tube is mounted'for a'sliding fit to permitexpansiou and contraction away from the rigid mounting of the combustor inlet tube and the inlet ejector tube during operation and shut-down.

The forward end of the pulse combustor inlet tube is provided with a fuel injector 22 of any suitable type positioned for injection into the tube a short'distance from the forward end which is inserted into the combustion chamber of a pulse jet combustor. The fuel injector has spray orifices extending therethrough directed toward the com bustion chamber. Thus the fuel injector is permitted to spray fluid fuel into the inlet tube wherein the fuel mixes with fresh air flowing in the combustor inlet tube toward the combustion chamber to form a combustible mixture. A fuel supply line 23 is connected to the fuel injector to supply a fluid fuel under pressure from any suitable systern.

For illustrative purposes, an air inlet system for use with a 3.5" valveless pulse jet can be made according to the dimensions shown in FIG. 1 for satisfactory operation in pulse jet engines as shown in FIGS. 2, 3 and 4 and adapted to a closed system such as for a turbine 35.

FIGS. 2, 3 and 4 illustrate different systems forusing the combustor air inlet system described above. In FIG. 2, the combustor air inlet system is adapted to a jetpulse combustor in which the inlet air and exhaust gases passing through the inlet ejector section is open to the atmos phere. In propulsion devices these gases will aid in propelling the device. As shown, thepulse jet combustor is f similar to that described in Patent No. 2,795,105 adapted with the air inlet and fuel mixing system according to the present invention,

The pulse jet'combustor is in the general form of a cylindrical tube closed at the forward end and open at the rear end, the forward portion being of relatively large diameter and short length to form a combustion cham- .P atented Sept. 5, 1961.

ber 18 having its exhaust section connected through a reducing portion with the rearward portion of smaller diameter and greater length to form a tail section 24. The tail section is open and flared at the rear end. rjor initial ignition of a fuel-air mixture in the combustion chamber, suitable ignition is provided in the form of a spark plug 25 which may be energized and controlled through any known or other suitable means not shown. The pulse combustor inlet tube 13 of the inlet air system is connected with the combustion chamber to supplythe air fuel mixture. Ignition means illustrated as a spark plug projecting into the combustion chamber, ignites the combustible mixture therein to initiate the Pulse action.

When the fuel-air mixture in the combustion chamber is ignited it burns and expands wherein the pressure in the tube forces the products out of the tube. One portion of the products of combustion leaves the tube through the open rear end while at the same time another portion of the expanding products leaves the combustion chamber at high velocities through the pulse combustion inlet tube and out through the inlet exhaust tube where the gas is discharged with considerable momentum in the ejector end of the inlet air system. The exhaust gas being discharged into the inlet ejector, sucks additional air through the plenum chamber surrounding the inlet tube. This induced air flow about the inlet exhaust tube into the inlet ejector carries with it any gases that may have escaped through the opening between the inlet tube and the exhaust tube. Consequently, the incoming fresh, cool air is maintained about the inlet tube opening for use by the combustor when needed for the next combustible reaction.

The outrush of the gas from the combustion chamber through the tailpipe of the pulse jet combustor causes overexpansion and a fall to subatmospheric pressure in the combustion chamber. The lowered chamber pressure produces a backflow in the combustor inlet tube which pulls fresh air at a high velocity into the inlet tube thereby permitting the fresh air to mix with the fuel at the forward end of the inlet tube to produce an explosive charge which flows into the compression chamber. In the meantime, the overexpanded tail gases come to rest, then rebound toward the combustion chamber to compress the fuel-air mixture and the residue of the previous explosion. The fresh charge begins to burn and the heat release is completed explosively as the previous cycle and the resonant cycle is repeated for continued operation of the pulse jet combustor. Both, air-fuel mixture pumping and ignition are carried out automatically by means of the resonant intermittent combustion cycle of about 100 cycles per second. The high frequency and broad positive pulse width enables the tail gas to drive into the discharge end to maintain a higher pressure than that at the inlet.

It is to be noted that the air inlet system provides in the plenum chamber a continued supply of fresh, cool air for the combustor inlet tube and the action of the inlet exhaust tube insures that no escaped combustion products are available to be sucked back into the air intake tube for the combustion chamber.

FIG. 3 illustrates a modification of the air inlet system which adapts the system to pipe the inlet exhaust gas-air mixture from the inlet ejector into the head end of a duct 31 surrounding the pulse jet burner to provide tube coolant flow along the combustor and tailpipe. The flow of the inlet exhaust gas-air mixture mixes with that from the tailpipe to provide backftow air for the combustion burner and to be injected into the gas flow from the tailpipe by direct action of the burner pressure waves. The coolant air also operates to lower the gasflow temperature of the tailpipe below the upper limit of the turbine to which the pulse jet combustor is connected.

Operation of any suitable array of valveless engines as for example, four with a common outlet will provide explosions that occur in a regular repetitive pattern with about degree phasing between the combustion chambers. Such an operation will provide a steady flow at the system discharge such that the pressure will be practically steady at the common outlet to supply a steady pressure flow at a turbine or at any other suitable device.

In the modification shown by FIG. 4, gas flow from the inlet air is connected with the forward end of the duct about thecombustor for cooling the combustor and mixed air-exhaust from the exhaust ejector is piped into the lowpressure region of the tail air ejector to be mixed with the mixed gas flow from the tailpipe to increase the pressure thereof and to cool the burner flow to usable temperature limits.

The design promoting the most duct-air incursion into gas flow of the tailpipe proved to be the one giving the most pressure rise percent of burner pulsation. As the fuel rate is raised above the lean operating limit, tube pulsation increases, which means an increase in the displacement of the gas column. This increases the backflow of the duct coolant air in the tail as the column rebonds with greater reverse-flow amplitude. matic increase of coolant air with increased heat addition is necessary to keep the gas-flow temperature below.

the upper limit of the turbine. For any given tail-ejector design it has been determined that pressure rise through the burner is almost linearly related to the percentage of cyclic pulsation in the combustion chamber of the main burner tube.

The air inlet system according to the present invention improves the operation and efiiciency of pulse jet engines and also enables one to use a pulse jet engine in a closed system such as for a turbine. system enables the operation of a pulse jet combustor to deliver hot gaseous products at a pressure above that of the inlet.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. In a valveless pulse jet engine comprising an elongated tubular structure having a closed forward end and an open end at the rear, a combustion chamber formed at said forward end, a combustion air inlet connected with said combustion chamber to admit fresh air into said combustion chamber, a housing secured about said combustion air inlet defining a plenum chamber, said housing including a main air inlet into said plenum and an air outlet, an inlet exhaust tube secured in said housing in axial alignment with said combustion air inlet and spaced axially therefrom with one end thereof adjacent thereto in end-to-end relationship, said combustion inlet tube operative relative to said inlet exhaust tube to permit a fresh air flow from said plenum directly into said combustion chamber and operative to eject combustion gases from said combustion chamber through said inlet exhaust tube and through said housing air outlet during use of the pulse jet.

2. In a valveless pulse jet engine comprising an elongated tubular structure having a closed forward end and an open end at the rear, a combustion chamber formed at said forward end, a combustion air inlet tube connected with said combustion chamber to admit fresh air into said combustion chamber, a housing secured about said combustion air inlet defining a plenum chamber, said housing including a main air inlet into said plenum chamber and an axially disposed outlet, an inlet exhaust tube and an inlet exhaust ejector section, said inlet exhaust tube secured in said housing in axial alignment with said combustion air inlet tube and spaced therefrom with one end thereof adjacent thereto in end-toend relationship, said inlet exhaust ejector section secured to the outlet of said housing in axial relationship therewith, said combustion inlet tube operative relative to said inlet exhaust. tube to This auto:

Also, the disclosed inlet permit a fiesh air flow from said plenum chamber directly into said combustion chamber and operative to eject combustion gases from said combustion chamber through said inlet exhaust tube and through said housing air outlet into said inlet exhaust ejector section during operation of said pulse jet.

3. In a valveless pulse jet engine as claimed in claim 2 wherein the adjacent ends of said combustion air inlet tube and said inlet exhaust tube are rigidly secured within said housing to maintain a constant spacing between the end-to-end spaced tubes.

4. In a valveless pulse jet engine comprising an elongated tubular structure closed at the forward end to form a combustion chamber and open at the rear end to permit a gaseous exhaust, a combustion air inlet tube connected with said combustion chamber to admit fresh air into said combustion chamber, a housing secured about said combustion air inlet defining a plenum chamber, said housing including a main air inlet into said plenum chamber and an axially disposed outlet, aninlet exhaust tube and an inlet exhaust ejector section, said inlet exhaust tube secured in said housing in axial alignment with said combustion inlet tube and spaced therefrom with one end thereof adjacent thereto in end-to-end relationship, and the other end extending into said inlet exhaust ejector, said inlet exhaust ejector section secured to the outlet of said housing in axial relationship therewith, said combustion inlet tube operative relative to said inlet exhaust tube to permit a fresh air flow from said plenum chamber directly into said combustion chamber and operative to eject combustion gases from said combustion chamber through said inlet exhaust tube and through said housing air outlet into said inlet exhaust ejector section during operation of said pulse jet, a duct of greater diameter than said tubular structure positioned about said elongated tubular structure with one end thereof connected with said inlet exhaust ejector section and the other end extending beyond said rear end of said elongated tubular structure whereby combustion gases and cool air from said plenum chamber passing through said inlet ejector section will be directed over said elongated tubular structure through said duct to function as a coolant.

5. In a valveless pulse jet engine as claimed in claim 4 wherein said inlet exhaust ejector section is connected with said closed duct forward of said combustion chamber.

6. In a valveless pulse jet engine as claimed in claim 4 wherein said air inlet is connected to said duct forward of said combustion chamber and said inlet exhaust ejector section is connected with said closed duct rearward of said combustion chamber.

References Cited in the file of this patent UNITED STATES PATENTS 2,770,226 Tenney Nov. 13, 1956 2,795,105 Porter June 11, 1957 2,812,635 Le Foll et al. Nov. 12, 1957 2,834,181 Paris et a1 May 13, 1958 2,919,542 Servanty et al. Jan. 5, 1960 (US. corresponding to British 786,232, Nov. 13, 1957) FOREIGN PATENTS 1,111,656 France Mar. 2, 1956 1,123,864 France June 18, 1956 786,232 Great Britain Nov. 13, 1957 

